Help with faulty TC Electronics XII phaser

[matlevo12]

Hi !

As advised by some smart souls on this forum I'm beginning a topic on this matter instead of trying to revive a 12 year old one.

I have a faulty TC Electronics XII phaser. It's a "Blue Classic" edition, not a BK or a Native.

The problem is there doesn't seem to be any LFO causing the phasing.
The LFO Speed and Width pots don't change a thing on the sound.
On the other hand the Filter 3 pos switch and the Function pot do work : you can hear differences on the guitar sound when you change them.

As I was looking for a schematic to help me I found this subject :
https://www.diystompboxes.com/smfforum/index.php?topic=61626

The person who started it seems to have a similar problem to mine... but the topic isn't closed and it doesn't say if he found a solution.
Here's the schem from that topic :
NB : The person did it himself , reverse engeneering it.
From what I observed (and read on the old topic) it seemed to me that the problem was coming from the top-right corner.
(nb : the schem is not correct, see post#2)

What I did first is test my luck : I had some LM339 from another project, I tried changing it but it didn't solve the problem.
(I know that was unlikely to work but I was a bit lazy...)

Then I began investigating with the schematic and test it on the circuit from my pedal.
The next thing I checked were the HEF4007UBT chip connections.
They all match the schematic except :
- pin 11 isn't connected to pin 1 and 12... and I can't seem to find where it's going
- pin 8 isn't connected to ground (or to the other end of D1 and R17, btw)
(nb : see post #2)
And that's it for the moment.

Does anybody have an idea on what I should test ?
I must admit I don't have a idea of what should be the voltages on pin 13 (that seems to be the LFO part output) or pin 1/12 (that seems to be the LFO+filter signal going out of the CD4007), but would that be helpful ?

Thanks a lot to anybody who reads this !

Bye !

Mat

[matlevo12]

Hi

Someone pointed a link on "the other website" to the service manual on the other topic, so now this makes more sense.
Here it is :



The schem from my previous post (from the 12 y.o. topic in reality) is not correct, mostly the CD4007 pin interconnections reflect one state of the pedal and pin 11 and 8 are just not used. I'll erase it.
But that let me realise something : my CD4007 chip is working properly so that isn't the problem.

Could anybody help me a bit to try and find what's wrong with this pedal and that it's not causing any phasing ?

[Fender3D]

Someone pointed a link on "the other website" to the service manual on the other topic, so now this makes more sense.

That someone was me...
You're welcome...

First: short 4007's pins 1 and 2, this will force "effect on"

2nd check voltage at Q4 base: it should move up and down

if you have a moving voltage @ Q4 you may have one or more vactrol dead, they are connected in series: if one dies the others won't work...
If you have a steady voltage @ Q4 check the program jack, it has 2 switches if they aren't ok LFO won't work.

[matlevo12]

That someone was me...
You're welcome...

Let me thank you in here as well then!
That's really helpful.
I'll check all this this weekend and write back the results!

Important note : my pedal is not the B/K version, it's mostly SMD components (except the vactrols, which is a good thing) and doesn't have a program jack.

[matlevo12]

The 4007 works perfectly so its pin 1 and 2 are connected when the effect is on.

Voltage at Q4 base is steady at 9V.

Since there isn't any program jack on my version of the pedal what would you recommend ?

[Fender3D]

I don't know if the SMD version is the same as the trough hole pedal....
I think you should post some voltage, especially around the 339...

Check if you have a moving voltage @ its output pins

[matlevo12]

Thanks a lot, again.

I don't know if the SMD version is the same as the trough hole pedal....

So far I'd say I've checked 60% of it and it's the same.

I think you should post some voltage, especially around the 339...
Check if you have a moving voltage @ its output pins

I had a quick look and nothing seems to move.

Values later tonght

[matlevo12]

All measured with speed at min and width at max.
Pin 1 : seems to move up everytime I measure it, from 70mv to 168mv in about 10s, then stays there.
Pin 2 : 3mv
Pin 3 : 9V (Vcc)
Pin 4 : 4,915V
Pin 5 : 4,894V
Pin 6 : 476mv
Pin 7 : 413mv
Pin 8 : 228mv
Pin 9 : 476mv
Pin10 : 334mv
Pin 11 : 476mv
Pin 12 : ground
Pin 13 : 610mv
Pin 14 : 473mv

At max rate the values are different but all still steady.

My guess is that the lm339 I used isn't working either, but how unlucky would that be, and but what do I know, huh?
What do you think?

Thanks again, a lot.

Mat

[Fender3D]

Pins 1, 14 and 13 are strangely low, despite the pull up resistors....
check the other side of those pull ups is actually at Vcc

[matlevo12]

Pins 1, 14 and 13 are strangely low, despite the pull up resistors....
check the other side of those pull ups is actually at Vcc

Hi,

I just checked and they're all at Vcc, and connected together.
I checked the connections between :
- pin 1 and D1, D1 and R48, R48 and R52 (there was 7,63 volts between R48 and R52, and 9,12V at the other end of R52)
- pin 14 and R53 (again 9V at the other end)
- pin 13 and R62 (again 9V at the other end)
- R52, R53 and R62
- some connections on the other side too (R49, C23, C24, etc)

[Fender3D]

At this point I don't know what it can be....
the first 2 comparators make the LFO the 3rd comparator and the following transistors make the wave hyperlogaritmic.
IIRW there should be ~0.5V waveform at first transistor's base.

If it's not the 339 check capacitors...

[matlevo12]

Thanks a lot, I'll try this asap.

[matlevo12]

Ha !

C24 was dead. I was running out of time but jsut had time to test it again afterwards : some variation at pin 14.
No result with the guitar and amp, but I'll check the other eletrolytics tomorrow.

Edit : It was the damned electrolytics !

5 of them were dead - or dying. I changed them temporarily with classic ones and the phaser works... surprising since the pedal is not that old.

Thanks a million @Fender3d !

[Fender3D]

You're welcome.
Glad to know it works now

Cheers

[boas]

Hi!
I was excited finding this thread, since my tc phaser xii b/k is no longer working (same problem as in this thread, with  speed and width pots not changing anything, but the filter and function change the sound).
Thanks for sharing your experiences.
The cd4007 looks slight injured at one of the pins in my pedal, and I hope this is why its not working. When I turn on the pedal, I measure 257 Ohms between pin 1 and 2 on the 4007, and when it is off, the pins are not connected. Do any of you know if this is indicating if it is faulty?

Hope the best!

[amptramp]

Hi!
I was excited finding this thread, since my tc phaser xii b/k is no longer working (same problem as in this thread, with  speed and width pots not changing anything, but the filter and function change the sound).
Thanks for sharing your experiences.
The cd4007 looks slight injured at one of the pins in my pedal, and I hope this is why its not working. When I turn on the pedal, I measure 257 Ohms between pin 1 and 2 on the 4007, and when it is off, the pins are not connected. Do any of you know if this is indicating if it is faulty?

Hope the best!

You should not use an ohmmeter on a unit that is switched on.  The ohmmeter works by applying a specific voltage to a resistor and measuring the current.  Connecting it to an operating circuit means this voltage is altered and unless you know the circuit inside the ohmmeter, you cannot determine the resistance.  Never use an ohmmeter on an operating circuit.

[boas]

@amptrap: Thanks for letting me know, I still have much to learn. I will read voltages then and report here like matlevo12 did.